Activation of CS₂ and CO₂ by Silylium Cations

The hydride-bridged silylium cation [Et₃ Si-H-SiEt₃ ]⁺ , stabilized by the weakly coordinating [Me₃ NB₁₂ Cl₁₁ ]^- anion, undergoes, in the presence of excess silane, a series of unexpected consecutive reactions with the valence-isoelectronic molecules CS₂ and CO₂ . The final products of the reaction with CS₂ are methane and the previously unknown [(Et₃ Si)₃ S]⁺ cation. To gain insight into the entire reaction cascade, numerous experiments with varying conditions were performed, intermediate products were intercepted, and their structures were determined by X-ray crystallography. Besides the [(Et₃ Si)₃ S]⁺ cation as the final product, crystal structures of [(Et₃ Si)₂ SMe]⁺ , [Et₃ SiS(H)Me]⁺ , and [Et₃ SiOC(H)OSiEt₃ ]⁺ were obtained. Experimental results combined with supporting quantum-chemical calculations in the gas phase and solution allow a detailed understanding of the reaction cascade.